Device for powdering printed sheets in a printing press, and printing press with a powdering device

ABSTRACT

A device for powdering a printed sheet in a printing press is formed with nozzle groups that are arranged in a row and that each are formed with several spray nozzles, each of which emits a powder/air mixture. A respective feed line is connected upstream of the nozzles of each nozzle group. The feed line of the spray nozzles of the respective nozzle group is preceded by a common collective line. Along a defined segment of a given length of the course of the respective collective line, a product of the radius of curvature of the segment and the fourth power of an inner diameter of the respective collective line equals 3.125×10 −10  m 5  at a minimum. In a preferred embodiment, the nozzle groups are nozzle heads.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C. §119, of Germanapplication DE 10 2010 032 644.5, filed Jul. 29, 2010; the priorapplication is herewith incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention:

The invention lies in the field of printing technology. Morespecifically, the present invention relates to a device for powdering aprinted sheet in a printing press comprising nozzle groups arranged in arow and each including several spray nozzles. Each of the spray nozzlesemits a powder/air mixture. A respective feed line is connected upstreamof the spray nozzles of the respective nozzle group and a commoncollective line is connected upstream of the feed lines of the spraynozzles of the respective nozzle group.

U.S. Pat. No. 5,713,285 describes a powdering device in which the nozzleheads are arranged in a row on a bar. Each of the nozzle heads comprisestwo spray nozzles preceded by a respective feed line which is internalrelative to the nozzle head. The two feed lines of the respective nozzlehead branch off of an upstream common collective line in a crotch. Thecollective line is designed as a hose. Each of the nozzle heads isconnected to a distributor by its own collective line. The distributorsupplies the powder/air mixture to the nozzle heads. Moreover, acompressor is provided to supply the pressurized air required to createthe powder/air mix. In the disclosed device, the efficiency of thepowder application leaves room for improvement.

U.S. Pat. No. 7,607,391 B2 and its counterpart German published patentapplication DE 10 2004 057 478 A1 describe a powdering device in whicheach of the nozzle heads comprises three spray nozzles with divergingspraying directions.

Commonly assigned U.S. Pat. No. 6,085,654 and its counterpart Germanpublished patent application DE 199 01 245 A1 describe a powderingdevice in which supply lines connected to a respective nozzle headbranch off from a distributor.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a powderingdevice for powdering sheets of a printing press which overcome theabove-mentioned disadvantages of the heretofore-known devices andmethods of this general type and which provides for a device forpowdering a printed sheet in which a high degree of efficiency of thepowder application is ensured.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a device for powdering printed sheets ina printing press, the device comprising:

a plurality of nozzle groups disposed in a row and each having aplurality of spray nozzles configured to eject a powder/air mixture;

a feed line connected upstream of each of said spray nozzles for feedingthe powder/air mixture to each respective spray nozzle;

a common collective line connected upstream of said feed lines of saidspray nozzles of the respective said nozzle group;

said common collective line having an inner diameter and extending alonga determined course with a segment thereof having a given radius ofcurvature; and

wherein, in said segment of the course of the respective said collectiveline, a product of said given radius of curvature and a fourth power ofsaid inner diameter of said collective line equals at least 3.125×10⁻¹⁰m⁵.

In other words, the objects of the invention are achieved with a devicefor powdering a printed sheet in a printing press comprises nozzlegroups arranged in a row, each group including several spray nozzles,each of which emits a powder/air mixture. A respective feed line isconnected upstream of the spray nozzles of the respective nozzle groupand is preceded by a common collective line. Within a given distance ofthe course of the respective collective line, a product of a radius ofcurvature of the course of the respective collective line and the fourthpower of an inner diameter of the respective collective line equals atleast 3.125×10⁻¹⁰ m⁵.

The degree of efficiency of such a device is very high. In such adevice, the number of powder particles applied to the sheet per unit ofsurface area is particularly high. The pressure of the pressurized airused to create the powder/air mixture does not need to be increased toincrease the degree of efficiency. Thus a comparatively low-cost aircompressor can be used.

In accordance with a further development of the invention each group ofspray nozzles that emit the powder/air mixture comprises at least threespray nozzles.

In accordance with another development of the invention the collectivelines of the nozzle groups branch off of a common distributor ormanifold.

In accordance with yet another development of the invention, the defineddistance of the course of the respective collective line equals at leasttwenty times the inner diameter of the respective collective line.

In accordance with again a further development, the spray nozzles of therespective nozzle group have mutually parallel spraying directions.

In accordance with yet another further development, the central axes ofthe feed lines of the respective nozzle group are aligned to be parallelto a central axis of the common collective line of these feed lines asviewed in the direction of travel of the sheet. In accordance with thisfeature, the feed lines of the respective nozzle group may be arrangedinternally with respect to this nozzle group.

In accordance with yet another further development, the central axes ofthe feed lines of the respective nozzle group are arranged at an anglerelative to a central axis of the common collective line of these feedlines as viewed in the direction of travel of the printed sheet. Inaccordance with this feature, the feed lines of the respective nozzlegroup may be arranged externally with respect to this nozzle group.

In accordance with a concomitant feature of the invention, the nozzlegroups are formed as nozzle heads. The nozzle heads may be fixed to asupporting cross bar such as a hollow profile.

The invention also relates to a printing press that is equipped with adevice for powdering a printed sheet in accordance with the invention asoutlined above or in accordance with one of the further developments.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a device for powdering a printed sheet in a printing press, it isnevertheless not intended to be limited to the details shown, sincevarious modifications and structural changes may be made therein withoutdeparting from the spirit of the invention and within the scope andrange of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 illustrates a powder device including nozzle heads arranged in arow;

FIG. 2 illustrates the connections of the nozzle heads of FIG. 1 with amanifold based on an exemplary nozzle head;

FIGS. 3 and 4 illustrate different views of a first exemplary embodimentof the nozzle head of FIG. 2; and

FIGS. 5 and 6 illustrate different views of a second exemplaryembodiment of the nozzle head of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawing in detail and first,particularly, to FIG. 1 thereof, there is shown a section of a printingpress 1. The illustrated section is an elevational view of a powderingdevice arranged in a sheet delivery of the printing press 1. Thepowdering device is used to powder the printed sheets that have beenfreshly printed in the press 1. The powdering device comprises a crossbar 2 extending over the entire printing width and carrying nozzle heads3 of identical construction. The nozzle heads 3 may also be referred toas nozzle groups. The nozzle heads are arranged in a row and have nozzleopenings that emit a powder/air mixture in a direction perpendicular tothe plane of FIG. 1. The nozzle openings of each nozzle head 3 aresupplied with a powder/air mixture by a respective system of lines 14.The structure of the line system 14 will be explained in more detailbelow.

FIG. 2 illustrates a manifold 4 for distributing the powder/air mixtureto several collective lines 5 each of which leads to a different one ofthe nozzle heads 3. The respective collective line 5 may be designed asa tube or preferably as a flexible, bendable hose. It includes a firstsection 6 and a second section 7. The first section is closer to themanifold 4 and is longer than the second section 7. The length of thesecond section 7 is described as a segment L whose length amounts to atleast twenty times an inner diameter d of the collective line 5. Theinner diameter d ranges between a minimum of 5 mm and a maximum of 50mm. In a preferred embodiment, the inner diameter d is approximately 20mm (approximately 0.8 inches) and thus the segment L is at leastapproximately 400 mm (approximately 16 inches). The segment L is limitedon one end by the end 8 of the first section 6 and on the other end by afork 9. The second section 7 immediately follows the end 8 of the firstsection 6 and has a curvature that is less pronounced than the curvatureof the first section 6 and may, in extreme cases, even be straight. Themagnitude of a radius r of curvature of the collective line 5 may varyalong the segment L but may not drop below 0.5 meters. The radius r ofcurvature starts in an imaginary center M of the curvature and ends at acentral longitudinal axis A of the collective line 5. The center M islocated outside the collective line 5.

In the fork 9, the system of lines 14 located between the manifold 4 andthe respective nozzle head 3 splits into several feed lines, in thegiven example into three feed lines 10, each of which leads to adifferent spray nozzle of a nozzle head 3 in question. The fork 9 may bereferred to as a distributor fitting and is inserted like a plug intothe end of the collective line 5 that is distal to the manifold 4. Thefork 9 has an end facing the feed lines 10. In this end, three smallnon-central bores are formed. A different one of the feed lines 10 istightly inserted into each of these bores. The other end of the fork 9has a large central bore which meets the three small bores. Due to thetransition between the large bore and a small bore the flowcross-section changes at least once between the manifold 4 and thenozzle head 3, even if the total cross-section may remain the same. Thelatter is the case if the flow cross-section of the large bore equalsthe sum of the flow cross-sections of the small bores. The main volumeflow of the powder/air mixture that enters the fork 9 through the largebore is evenly distributed in the fork 9 to provide an identical partialvolume flow of the powder/air mixture that exits each of the smallbores. The Reynolds number of the collective line 5 and of the secondsection 7 in particular is at least 2300.

This feature ensures that there are turbulent flow conditions in thecollective line 5 and in the second section 7 in particular,advantageously promoting a randomly even distribution of the amount ofpowder to the feed lines 10.

The fact that the product of the radius r of curvature and the fourthpower of the inner diameter d equals at least 3.125×10⁻¹⁰ m⁵ along thesegment L immediately upstream of the fork 9 ensures that, unaffected bythe turbulences and, in fact, potentially even enhanced by them, themain volume flow is split into partial volume flows of equal magnitude.Thus all the spray nozzles of the nozzle head 3 are supplied with equalamounts of powder.

By way of example, FIG. 3 illustrates one of the nozzle heads 3 of FIG.2 as viewed in a direction III-III in FIG. 4. FIG. 4 illustrates thesame nozzle head 3 as viewed in a direction IV-IV in FIG. 3. The nozzlehead 3 includes several spray nozzles 15; in the given example, thereare three spray nozzles 15, whose spraying directions are mutuallyparallel or at least substantially parallel. As each of the nozzle heads3 includes several spray nozzles 15, the nozzle heads 3 may also bereferred to as nozzle groups. Accordingly, an angle located betweenimaginary central axes 16 of nozzle bores or nozzle channels of thespray nozzles 15 is preferable 0°. The central axes 16 of the two outerspray nozzles 15 may diverge slightly, defining an angle not greaterthan 5°. A non-illustrated transport device, for instance a chainconveyor, moves a printed sheet 17 past the nozzle heads 3 in adirection of travel 18 that is perpendicular to the plane of the drawingof FIG. 4. The direction 18 of travel is indicated symbolically by anarrow in FIG. 3 but not specifically illustrated in FIG. 4. The spraynozzles 15 emit spray jets 19 that widen conically and hit the surfaceto be powdered of the printed sheet 17 perpendicularly or at leastsubstantially perpendicularly. As can be seen in FIG. 3, thelongitudinal axes or central axes 20 of the feed lines 10 are orientedat an angle—preferably a right angle—relative to the longitudinal axis Aor central axis A of the collective line 5 to which the aforementionedfeed lines 10 are connected by way of the fork 9. For the major part,the feed lines 10 are located outside the nozzle head 3. They may bedesigned as tubes or, preferably, as flexible, bendable hoses. Thecentral axis 20 of that section of the feed line 10 that is immediatelyconnected to the nozzle head 3 is oriented at an angle—preferably aright angle—relative to the longitudinal or central axis A of the secondsection of the collective line 5.

FIG. 5 illustrates one of the nozzle heads 3 of FIG. 2 as viewed in adirection V shown in FIG. 6. FIG. 6, on the other hand, illustrates thesame nozzle head 3 as viewed in a direction VI shown in FIG. 5. In thisexemplary embodiment, each nozzle head 3 likewise includes a pluralityof spray nozzles 15, preferably three spray nozzles 15. The spraynozzles 15 have mutually parallel spraying directions and thus mutuallyparallel central axes 16. The spraying directions are determined by thenozzle bores or nozzle channels of the spray nozzles 15. The nozzlechannels have central axes 16 that are oriented perpendicularly (at a90° angle) or substantially perpendicularly (90°±2.5°) to the surface tobe powdered of the printed sheet 17. The spraying directions of the twoouter spray nozzles 15 of the respective nozzle head 3 may divergetowards the printed sheet 17 at an angle of divergence not greater than5° between the central axes 16 of the two outer nozzles. In FIG. 5, theangle is 0°, i.e. the central axes 16 of the outer nozzles are parallelto each other and parallel to the central axis 16 of the inner nozzle.

In contrast to the exemplary embodiment of FIGS. 3 and 4, the exemplaryembodiment illustrated in FIGS. 5 and 6 features feed lines 10 that areintegrated into the nozzle head 3. The respective spray nozzle 15 andthe feed line 10 corresponding with this spray nozzle 15 form one andthe same channel, which may be formed by a single bore in the case ofthe inner nozzle and by two respective meeting bores in the case of theouter nozzle. The fork 9 is immediately connected to the nozzle head 3or is formed integrally in one piece with the latter. The central axes16 of the spray nozzles 15 are oriented perpendicularly to the directionof travel 18 of the printed sheet 17. As viewed in the direction oftravel 18 of the printed sheet 17, the central or longitudinal axis A ofthe second section 7 is oriented at an angle relative to the centralaxes 20 of the two outer feed lines 10 and the central axis 20 of thecentral inner feed line 10 is in alignment or parallel.

In accordance with a non-illustrated modification, the nozzles 15 of allthe nozzle groups are not formed in nozzle heads attached to the crossbar 2, but are formed in the cross bar 2 itself, which then acts as aso-called spray bar.

1. A device for powdering printed sheets in a printing press, the devicecomprising: a plurality of nozzle groups disposed in a row and eachhaving a plurality of spray nozzles configured to eject a powder/airmixture; a feed line connected upstream of each of said spray nozzlesfor feeding the powder/air mixture to each respective spray nozzle; acommon collective line connected upstream of said feed lines of saidspray nozzles of the respective said nozzle group; said commoncollective line having an inner diameter and extending along adetermined course with a segment thereof having a given radius ofcurvature; and wherein, in said segment of the course of the respectivesaid collective line, a product of said given radius of curvature and afourth power of said inner diameter of said collective line equals atleast 3.125×10⁻¹⁰ m⁵.
 2. The powdering device according to claim 1,wherein a number of said spray nozzles for emitting the powder/airmixture per nozzle group is at least three.
 3. The powdering deviceaccording to claim 1, which comprises a common manifold, with saidcollective lines of said nozzle groups branching off from said commonmanifold.
 4. The device according to claim 1, wherein a length of saidsegment of said course of the respective said collective line amounts toat least twenty times said inner diameter of the respective saidcollective line.
 5. The device according to claim 1, wherein said spraynozzles of the respective nozzle group have mutually parallel sprayingdirections.
 6. The device according to claim 1, wherein said feed linesof a respective said nozzle group have central axes aligned to beparallel to a central axis of said common collective line as viewed in adirection of travel of the printed sheets.
 7. The device according toclaim 6, wherein said feed lines of a respective said nozzle group arearranged internally in said nozzle group.
 8. The device according toclaim 1, wherein said feed lines of a respective said nozzle group havecentral axes arranged at an angle relative to a central axis of saidcommon collective line for said feed lines, as viewed in a direction oftravel of the printed sheets.
 9. The device according to claim 8,wherein said feed lines of the respective said nozzle group are arrangedexternally with respect to said nozzle group.
 10. The device accordingto claim 1, wherein said nozzle groups are nozzle heads.
 11. A printingpress, comprising a device according to claim 1 disposed to powderfreshly printed sheets.